This invention relates to an improved process for making diglycidylether of alkoxylated resorcinol using novel catalysts. In particular, it has been discovered that halides of indium, antimony and tellurium are effective catalysts for the preparation of the epoxy resins of the present invention.
Epoxy resins are an important class of thermosetting polymers that exhibit properties such as high tensile strength and modulus, chemical and corrosion resistance and dimensional stability. Due to these excellent mechanical properties, epoxy resins are used in a wide range of industrial applications, including structural adhesives, coatings, and matrix resins in fiber reinforced composites.
Epoxy resins based on bisphenol A are well known and have been used extensively in various industrial applications. However, epoxy resins based on resorcinol offer additional advantages, as compared with those based on bisphenol A, as they have low viscosity and high reactivity toward various curing agents. In particular, resorcinol diglycidylether resin shows excellent cured physical and mechanical properties.
Unfortunately, resorcinol diglycidylether (RDGE) has been reported to cause skin cancer. Epoxy resins based on derivatives of resorcinol have been developed which provide similar mechanical properties as resorcinol diglycidylether but with lower toxicity. For example, U.S. Pat. No. 5,300,618 discloses epoxy resins based on 4-benzoyl resorcinol.
In the development of carbon fiber reinforced composites, epoxy resins are often cured with aromatic diamines to achieve high glass transition temperature and enhance cured resin mechanical properties. The diamine curing agents often produce high crosslink density in the cured epoxy resins, which results in low impact strength due to brittleness. To overcome this problem, toughening agents are used to improve the impact strength and fracture toughness of cured epoxy compounds. For example, U.S. Pat. Nos. 4,656,207 and 4,656,208 disclose the use of an amine terminated poly(arylether sulfone) oligomeric modifier in the development of carbon fiber reinforced composites using a resin material sold under the trade name Heloxy 69 (RDGE). European Patent 0 679 165 also discloses toughened epoxy resin systems based on substituted resorcinol-based epoxy resins and amine terminated poly(arylene ether sulfone) oligomers.
Decreasing the crosslink density in the final material can minimize the brittle character of cured epoxy resins, including resorcinol diglycidylether. This can be achieved by increasing the distance between the two epoxy groups through the introduction of linear alkyl or alkyl ether groups. The introduction of an alkylene ether group in the epoxy molecule can best be done by alkoxylating the aromatic dihydroxy compounds first, using the alkylene oxides or carbonates, before the glycidylether reaction with epichlorohydrin. Use of epoxy resins and epoxy hardeners or curing agents having such flexible akyl ether groups improves the toughness of the cured epoxy system by reducing its brittleness.
Various industrial processes and methods are known for the synthesis of bis(hydroxy ethylated) or bis(hydroxy propylated) aromatic dihydroxy compounds, using either carbonates such as ethylene or propylene carbonate, or oxides such as ethylene or propylene oxide. For example, U.S. Pat. No. 5,059,723 discloses the synthesis of bis(hydroxy ethyl) ether resorcinol from the reaction of resorcinol with ethylene carbonate. U.S. Pat. No. 6,303,732 also discloses various reaction schemes for the preparation of aromatic diols from the resorcinol and ethylene or propylene carbonate reaction. These resorcinol based aromatic diols can be used to synthesize the corresponding diglycidylethers for various high performance applications including coatings, adhesives and composites.
The synthesis of diglycidylether of alkoxylated resorcinol using an excess of epichlorohydrin has been reported. For example, Soviet Union Patent 702017 discloses the synthesis of diglycidylether of bis(hydroxy ethylated) resorcinol for high impact resistance epoxy polymers, using almost a 10-fold excess of epichlorohydrin. The method of this patent does not use a catalyst; resorcinol is reacted with ethylene chlorohydrin and sodium hydroxide in the presence of isopropyl alcohol to produce bis(hydroxy ether) resorcinol. The resulting compound is then reacted with an excess of epichlorohydrin and solid sodium hydroxide to prepare the epoxy resin.
A process in which an excess of epichlorohydrin is used may not be economical for the commercial production of epoxy resin due to the formation of sodium chloride and the added need to separate sodium chloride from the resorcinol and ethylene chlorohydrin reaction system. Additionally, the use of large quantities of epichlorohydrin and the handling of solid sodium hydroxide in the epoxy reaction are undesirable due to the hazardous nature of these materials.
To overcome the problems associated with using a large excess of epichlorohydrin, new methods and process conditions have been developed. For example, the use of hydroxy aromatics and hydroxy alkylated aromatics as starting materials permits the use of stoichiometric amounts of epichlorohydrin. However, in the case of hydroxy alkylated aromatics, special catalysts and process conditions are required to promote the reaction between hydroxy alkylated aromatics and epichlorohydrin, due to the more aliphatic nature of the hydroxy group; typically, a Lewis acid-type catalyst such as AlCl3, ZnCl2, FeCl3, SnCl4 and BF3 is used.
Various patents disclose the use of these catalysts. For example, U.S. Pat. No. 4,507,461 discloses the preparation of epoxy resins from the propoxylated bisphenol A and epichlorohydrin using boron trifluoride (BF3) catalyst; U.S. Pat. No. 5,162,547 discloses the preparation of epoxy resins from the aliphatic polyols such as 1,4-butanediol, trimethylol propane, sorbitol, 1,4-cyclohexane diol, etc., using tin (II) halides, preferably a tin (II) fluoride catalyst, in the presence of xylene and MIBK solvents; U.S. Pat. No. 5,227,436 also discloses the synthesis of epoxy resins from the oxyalkylated bisphenol A, prepared from bisphenol A and an alkylene oxide, and epichlorohydrin using tin (IV) chloride catalyst in the presence of methyl isobutyl ketone (MIBK) solvent; U.S. Pat. No. 5,245,048 discloses the use of perchlorate or trifluoromethane sulfonate salts of lantharium, cerium, ytterbium or yttrium as the catalysts for the epoxy resins from the aliphatic diols; and U.S. Pat. No. 5,342,903 discloses the preparation of epoxy resins from the aliphatic diols such as 1,4-butanediol, 1,4-cyclohexanediol, etc., employing lanthanide and actinide salts as the catalysts.
In spite of the above methods, there continues to be a need for novel methods and catalysts for making diglycidylether of alkoxylated resorcinol, using stoichiometric amounts of epichlorohydrin.
Accordingly, the present invention provides a method of preparation of diglycidyl ethers of the following formula: 
where R=an ethoxy or propoxy group and n=1 to 3 comprising:
(a) mixing a dihydroxy aromatic compound with an alkylene carbonate in the presence of a triorganophosphine catalyst using a stoichiometric excess of alkylene carbonate;
(b) reacting the mixture of step (a) at a temperature sufficient to initiate and maintain evolution of CO2 for a length of time sufficient to achieve the reaction of said dihydric phenol and said alkylene carbonate to produce an aromatic diol;
(c) reacting the product of step (b) with an epihalohydrin, in the presence of a second catalyst selected from the group consisting of antimony halide, indium halide and tellurium halide, at a temperature sufficient to allow the reaction to occur;
(d) cooling the mixture of step (c) to xe2x89xa6100xc2x0 C.;
(e) adding a solvent to the mixture of step (d);
(f) adding a caustic to the mixture of step (e);
(g) adding water to the mixture of step (f); and
(h) allowing the mixture of step (g) to settle for an amount of time sufficient to permit phase separation to occur.
Using the above method, stoichiometric amounts of the epihalohydrin can be used, avoiding the undesirable effects of an excess of this compound. The above described method provides a cost effective means of producing diglycidylether of alkoxylated resorcinol, without the need to remove excess amounts of the epihalohydrin.
It has been found that antimony, tellurium and indium halides are able to function as efficient catalysts and provide a sufficient yield of the desired end product.
It is an object of the invention, therefore, to provide a novel process for producing diglycidylether of alkoxylated resorcinol, using catalysts not previously known in the art as useful for this process.
It is an additional object of the present invention to provide a cost effective and less hazardous means of producing diglycidylether of alkoxylated resorcinol.
These and other objects of the invention will become more readily apparent from the following drawing, detailed description, examples and appended claims.